1. Field of the Invention
Embodiments of the present invention relate generally to a semiconductor manufacturing apparatus. More particularly, embodiments of the invention relate to a wafer loading apparatus adapted to prevent local defocus in the semiconductor manufacturing apparatus.
A claim of priority is made to Korean Patent Application No. 2005-31155, filed on Apr. 14, 2005, the disclosure of which is hereby incorporated by reference in its entirety.
2. Description of Related Art
Semiconductor manufacturing apparatuses commonly use photolithography processes to form patterns on the surface of a wafer. A photolithography process generally includes a number of processing steps, which are performed in a sequence. The processing steps may include, for example, substrate preparation, photoresist application, soft-baking, exposure, developing, hard-baking, and etching.
Since these processing steps are generally performed in a sequence, errors in early processing steps tend to cause problems in later steps. For example, if photoresist application is performed incorrectly, soft-baking, exposure, and so forth will also be affected.
One problem that commonly occurs in the exposure step of photolithography processes is known as “local defocus”. Simply stated, the “local defocus” problem occurs when the light used to expose the photoresist in the exposure process is out of focus in some local region of a wafer. One way that local defocus can occur is where the wafer itself has local distortions (See, for example, FIG. 4). One source of local distortions of the wafer is contamination particles deposited on a wafer loading apparatus. The contamination particles can cause the local distortions in the wafer by pushing upwards on the wafer.
Local defocus can be prevented by frequently cleaning the surface of the wafer loading apparatus where the wafer is mounted. However, frequently cleaning the wafer loading apparatus takes a significant amount of time and tends to deteriorate the efficiency and productivity of the semiconductor manufacturing apparatus. As a result, frequently cleaning the wafer loading apparatus is not a desirable solution for reducing local defocus.
Another way to reduce local defocus is to include a plurality of protrusion elements (also referred to as pimples or burls) in the wafer loading apparatus to reduce the surface contact area between the wafer loading apparatus and a loaded wafer. By reducing the surface contact area between the wafer loading apparatus and the loaded wafer, the amount of contamination that touches the loaded wafer is greatly reduced. Unfortunately, this method cannot entirely eliminate local defocus caused by particles on the wafer loading apparatus because portions of the protrusion elements in contact with the wafer may still contain particles.
Referring to FIGS. 1 and 2, a conventional wafer loading apparatus 10 in a wafer alignment and exposure device comprises a plate 16 including an edge area 14 and a center area including a plurality of protrusion elements 20. Wafer loading apparatus 10 further comprises a plurality of support pins 12 adapted to support a wafer.
Protrusion elements 20 define an even contact plane adapted to support a bottom surface of a loaded wafer for an exposure process.
Referring to FIG. 3, wafer loading apparatus 10 includes protrusion elements 20a and 20b extending from respective top and bottom surfaces of plate 16. Protrusion elements 20a support the loaded wafer, while protrusion elements 20b contact a chuck (not shown), which holds plate 16.
As shown in FIG. 4, a particle 4 located on one of protrusion elements 20 distorts the contact plane between a wafer 2 and the wafer loading apparatus. The distorted contact plane causes local defocus in a subsequent exposure process, which may cause a bridge or an abnormal photoresist pattern to form on the loaded wafer.
Local defocus occurs on a regular basis in alignment and exposure devices such as those illustrated in FIGS. 1 through 4. For example, Table 1 shows instances of local defocus that occurred in a semiconductor manufacturing apparatus between Jun. 1, 2004 and Sep. 30, 2004. The average number of local defocus problems and damaged wafers per month as shown by Table 1 is 253 and about 578, respectively, and about 9 to 10 wafers are damaged per each local defocus occurrence.
As suggested by Table 1, the conventional wafer loading apparatus is highly susceptible to process defects and wafer damage resulting from local defocus. Because of this, the local defocus problem tends to undermine the productivity of semiconductor manufacturing apparatuses that include the conventional wafer loading apparatus.
TABLE 1Number ofNumber ofInspection PeriodOccurrencesWafers(Year of 2004)of Local DefocusContaminatedJune 1~June 30195512July 1~July 31159413August 1~August 31394888September 1~September 30264500